JP7228050B2 - Methods and tools for measuring bone quality - Google Patents

Description

The present invention relates to the field of surgery, and more particularly to the field of dental surgery and implantology.

In the context of methods for determining bone quality, it is possible to classify two types of assessment methods. On the one hand, invasive methods, i.e. based on empirical data obtained during bone drilling to assess quality, and on the other hand, medical imaging techniques such as, for example, X-ray or magnetic resonance imaging (MRI). There are non-invasive methods that are used.

A method for assessment of bone quality (ie mechanical resistance) performed during site preparation for implant placement is described in patent document WO2008052367. This document specifies making a hole in the bone and then using a specific instrument to characterize the mechanical resistance of the bone. The properties characterized are, on the one hand, the mechanical deformation induced by the pressure exerted inside the hole and, on the other hand, the torsional moment or torque applied to the tool inserted in the hole to mechanically deform the hole. is.

A similar method employed at this time for large bones such as the femur is disclosed in document WO2012083468, which also discloses a handpiece adapted for this procedure. ing. In this case, the mechanical resistance of the bone is measured by rotating the drilling tool in the direction opposite to the drilling direction in order to correlate the mechanical deformation of the hole with the applied torque. The drilling tool also has a symmetrical form, which means that it can extract material in two rotational directions, a first direction for cutting and a second direction for measuring. means For this reason, this method is not suitable in the case of dental implants, since counter-rotation for measurement carries the risk of crushing or damaging the bone. Virtually all drill bits and drills for the preparation of dental implants have a threading direction and an unscrewing direction, which allows removal of the drilling tool without causing detachment of bone material. enable

US Pat. No. 7,878,987 proposes, in part, a unique alternative solution for minimally invasive assessment of whole bone resistance to fracture. In this case, the system can pass through the patient's skin and soft tissue before reaching the surface of the bone. Measurements are then taken by pushing a very fine test blade/probe inside the bone (into the indentation, without rotating the probe). By measuring the force applied to the blade/probe to penetrate and extract the bone, it is possible to establish an assessment of the risk of fracture of the bone.

However, there are no methods specifically employed in dental implantology for assessment of bone quality.

Currently, in this particular technical field, the only recognized method for qualitative assessment of bone quality of bone for dental implants is a non-invasive method as described below.
- Patent document JP2000245736 describes a tool for detecting osteoporosis using microwaves.
- US Pat. No. 6,763,257 to ROSHOLM et al. describes a method of bone quality assessment using radiograms.
- US Patent Application Publication No. 2003/0057947 to NI ET et al. describes a magnetic resonance-based technique for determining bone porosity.

However, these non-invasive methods do not provide a quantitative measure of bone quality and thus they do not allow defining a sufficiently precise spatial profile of bone quality to define implant strategies. It is considered too low precision to be used for

A need therefore exists for a solution that does not have these known limitations.

WO2008052367 International Publication No. 2012083468 U.S. Pat. No. 7,878,987 JP-A-2000245736 U.S. Pat. No. 6,763,257 U.S. Patent Application Publication No. 2003/0057947

The object of the present invention is to propose a new measuring device and a new method for determining bone quality, which is more precise and more efficient.

More specifically, it is an object of the present invention to provide well-defined spatial profiles of different bone regions without requiring additional measurement steps or requiring special instruments or special manipulations with respect to normal operating procedures. It is to be.

This object is achieved by the features of claim 1 of the main device.

The advantage of the proposed solution is that it introduces a method that allows quantitative measurement of bone quality during drilling for site preparation of dental implants. This procedure adds a standard implant kit consisting of a micromotor and a contra-angle reducer (usually with a gear ratio of 20:1) to a unique device. It can be used without need.

Moreover, such a method allows a series of measurements to be performed during all stages of implant preparation without the need to add supplemental work steps or to subject the patient to work that is more invasive than conventional drilling. becomes possible. In particular, deformation by pressure and/or torsional forces (as required in the context of the solution disclosed in WO2008052367) is not necessary.

Another important advantage offered by the proposed solution relates to the accuracy of the proposed quantitative measurements. In other words, this proposed quantitative measure allows not only to classify bone quality at the implant site, but also to reconstruct the spatial profile of bone quality from the bone surface to its depth. More specifically, the measurements obtained provide a precise spatial profile of bone quality from the surface of the bone to the interior of the bone, starting with the cortical region, the hardest region near the outer surface of the bone, and moving toward the bone. Identify the transition zone to the softer cancellous or apical region inside the .

According to a preferred embodiment of the present invention, bone quality is derived directly from current derivative measurements without directly measuring current. This allows the calculation process to be simplified and eliminates the need to post-process the current signal to obtain the torque value and thus the derivative of the torque that provides bone quality.

According to another preferred embodiment of the invention, the drilling tool has a variable diameter profile ranging between a minimum value and a maximum value, the ratio between the minimum value and the maximum value being at least 2 be equivalent to. In this case, it can be assumed that the current and torque derivatives depend only on the part of the drilling tool that has the diameter maximum. The quantity L _F (or L _f ) defines the length of the portion with the largest diameter. The ratio between the maximum and minimum diameters should be 2 or more to ensure that the spatial behavior of the current derivative depends only on the penetration depth of the maximum diameter portion of the drilling tool.

According to yet another embodiment of the present invention, the device for measuring bone quality further comprises an angular sensor such as a Hall sensor, magnetic sensor, optical sensor or electrical sensor to know the correct orientation of the rotor of the contra-angle. A sensor and an orientation determination system are provided to determine the correct orientation of the drill bit. It is thus possible to obtain an additional angular distribution of bone quality while ensuring that sufficient measurement data, for example of the order of 10, are collected for each full revolution of the drill bit.

Still in accordance with a further embodiment of the present invention, an apparatus for measuring bone quality comprises a non-circular asymmetric drill bit providing an extruded diameter at least 20% greater than the intermediate diameter of the drill bit. With such a special drilling tool it is possible to obtain a 3D representation of the bone quality, because it is possible to see variations in bone quality not only as a function of penetration depth, but also as a function of angular orientation. It's for.

According to a variant embodiment of the invention, the device for measuring bone quality further comprises a calibration and benchmarking tool to define classification criteria with a specific drill bit, handpiece or motor. can be made possible.

The invention will be better understood by reading the following description, given by way of example, with reference to the figures.

1 is a logical schematic diagram of various functional parts of a measuring device according to a preferred embodiment of the present invention; FIG. 1 is a schematic diagram of a drill bit conventionally used in the field of dental implantology; FIG. FIG. 3 is a cross-sectional view of the artificial bone highlighting the cortical and cancellous zones. 4 is a graph of current consumption of a motor according to the invention for two different types of bone prostheses as a function of time; 4 is a schematic diagram of torque exerted by a motor as a function of depth within each of two bones, according to an embodiment of the invention; FIG. 1 is a diagram of one type of drill bit that can be used in the context of the present invention; FIG. Figures 4A and 4B are diagrams of different types of drill bits that can be used in the context of the present invention; FIG. 4 is a state diagram showing how bone quality values are produced directly as a function of derivatives of current values, according to a preferred embodiment of the present invention; 3C is a graph of the current derivative of the current consumed by the motor for the two different types of bone prostheses previously shown in FIGS. 3A and 3B as a function of depth; FIG. 5 is a schematic diagram of the resulting bone quality as a function of depth within each of the two further bones. FIG. 6B is the same view as _FIG . 6A showing when the drilling operation is performed by a special drill, such as the one shown in previous FIG. Figure 6B is the same view as Figure 6B, showing when the drilling operation is performed by a special drill, such as the drill shown in previous Figure 4a, with a maximum diameter _Lf equal to a length of 0.5 mm; FIG. 3 is a sagittal section of the transitional region between the cortical and cancellous regions of bone. FIG. 8B is a horizontal cross-sectional view along the horizontal plane AA shown in FIG. 8A; 1 is a sagittal cross-sectional view of a handpiece fitted with a drill bit and equipped with an angle sensor in accordance with a preferred embodiment of the present invention; FIG. FIG. 10 is an enlarged view of this angle sensor mounted on the handpiece; Fig. 2 is a side view of a handpiece according to a preferred embodiment of the invention with an asymmetrical drill bit; FIG. 4 is a schematic diagram of a calibration tool, according to another preferred embodiment of the present invention;

In the context of the present application, the expression "contra-angle" is used as a generic term to denote the working tool of the practitioner, especially the dentist. Similarly, the term "motor" refers to the mechanical movement (especially rotary movement) transmitted to the drilling tool by means of a kinematic chain incorporated in a contra-angle having a transmission that determines a given deceleration factor. but in some cases represents in general form a device capable of producing linear, oscillatory, etc. motion). The expressions "drill bit" or "screw tap" are used as generic terms to denote any tool for drilling bone, regardless of model and dimensional characteristics.

Described below are preferred embodiments relating to the field of dental implantology. Such an electronic device for controlling a motor for implant surgery consists of a connection box with the motor and a peripheral device interface for the user (the two being detachable from each other or detachable by the user). can be incapable), characterized by the following characteristics:
1. A user-selectable feature activates the recording of the current consumed by the motor instantaneously, ie in real time.
2. Within the memory of this box or peripheral device, a post-processing algorithm, described below, converts the real-time signal of the current consumed by the motor into the torque applied to the drilling tool as a function of position in the depth of the tool. signal.
3. A tool for transmitting data to another electronic device is a communication gate via a WIFI emitter or cable.

The device and measurement method are shown schematically in FIG. 1, which shows the device with the transmission chain from the motor to the drilling tool applied to the bone and the return of the measurement data. The solid arrow indicates the direction of motion transfer and the opposite dashed arrow indicates the direction of transfer of information on energy consumption. In this figure, the transmission over the communication interface is performed wirelessly (lightning bolt indicating communication by any suitable technology such as Wi-Fi, UWB, etc.) and according to this preferred embodiment the current consumed by the motor A functional unit for the instantaneous measurement of is structurally integrated in the box of the controller. According to a variant, this unit can also be miniaturized and integrated into the motor.

During the procedure for measuring the bone quality of the dental implant site, the user of the implantology kit can first select an option via the control console of the motor, thereby obtaining the bone required for the preparation of the implant site. During at least one of the drillings, the current consumed by the motor is recorded in the memory of the motor junction box or peripheral device (eg, digital tablet) used as an interface. A control console (not shown) preferably includes a display unit in the form of an LCD screen and keys or wheels for selecting menus and/or programs and verifying selections made by the surgeon.

The real-time signal of the current consumed by the motor is then post-processed by an algorithm preferably installed on the motor connection box or peripheral used as an interface. Accordingly, in such a preferred embodiment, a unit for processing data collected during the drilling operation is incorporated within this box, although depending on the need and processing power constraints, a remote A processor located within the computer can also be used. In this case, however, the interface for data transfer must offer a sufficiently high speed so as not to constitute a limiting factor. Signal processing can use, for example, local regression methods, Savitzky-Golay methods, moving averages, Gaussian filtering, and the like. According to an advantageous embodiment, the signal processing can also eliminate stationary contributions related to the no-load consumption of the motor and the pressure exerted by the user, which stationary contributions are in effect "offsets". , ie constitutes only a constant shift of the immediate consumption curve.

Each of the motors has a power rating in watts, which constitutes the maximum possible power that this motor can generate. Normally, during the drilling phase, the power used, which can be determined directly from the current value since the voltage itself remains constant, does not exceed 10-15% of this rated power. Conversely, considerably higher values of up to 80% or even more of this rated power can be reached during the screwing phase of the implant.

With the current post-processed signal first establishing a relationship between the immediate power of the motor and the immediate torque exerted by the drill bit on the bone via the kinetic chain of the transmission, the second , it is then possible, using the drill bit type and drilling speed, to express the torque applied to the drilling tool as a function of position in the depth of this tool; Recorded in the memory of a box or peripheral, or transmitted to another electronic device by cable or WIFI.

In other words, the speed of the motor, typically between 100 and 1000 revolutions per minute (rpm), which is usually applied via a specific program and controlled by the console, is less than 1% during the drilling operation. On the one hand, this motor speed has very little deviation, on the other hand, the gear ratio of the contra-angle used (usually 20:1) and the drill bit used as drilling tool, especially its thread allows to clearly correlate the drilling time with the relevant depth.

Thus, as can be seen in the light of the correspondences of FIGS. 3a and 3b, the proposed method of bone quality determination allows transforming input data consisting of:
i. post-processed signal of current,
ii. drilling tool model used,
iii. The following output data, in particular the working speed of the motor:
a. signal of bone quality as a function of depth inside the bone,
b. the depth of the transition between the cortical and cancellous regions of the bone;
c. average bone quality within cortical regions,
d. average bone quality within the cancellous region,
e. Numeric confidence factor between 0 (low confidence) and 1 (high confidence) for mean bone quality values within cortical regions. In a preferred embodiment, this coefficient is a function of the correlation coefficient between torque and depth within the cortical region, the residual of the polynomial regression within the cortical region, and the signal-to-noise ratio within the cortical region.
f. Numeric confidence factor between 0 (low confidence) and 1 (high confidence) for mean bone quality values within the cancellous region. In a preferred embodiment, this coefficient is the correlation coefficient between torque and depth in cortical and corpus cavernosum regions, the residual of polynomial regression in cortical and corpus cavernosum regions, the signal to noise in cortical and corpus cavernosum regions. is a function of the ratio. Reliability in the corpus cavernosum region is usually low, as the calculation relies on the quality of the signal in two regions: the cortex and the corpus cavernosum. However, the method described makes it possible to mathematically quantify the degree of reliability within this region.

Figure 2a shows a typical drilling tool (screw tap), the drilling length of which is about 8 mm and stops at 12 mm, while Figure 2b shows a commercially available prosthesis (similar to real bone composition). showing bones. This bone has a 4 mm denser hard region combined with a 11 mm softer region.

In Figures 3a and 3b an example of post-processed measurements according to the method described above is shown.

The signal of current consumed as a function of time shown in FIG. 3a is post-processed and inferred from FIG. It was also linked to the signal of torque as a function of bone depth at the tip of the drilling tool. Separate measurements shown in the two overlaid graphs in each of these Figures 3a and 3b were made for the two types of artificial bone.
- Type 1: cortical area thickness equal to 6 mm and high quality cancellous areas.
- Type 4: thickness of cortical area equal to 1 mm and cavernous area of poor quality.

Parameters describing the output data can be viewed directly on the graph.
- Artificial bone 1 and artificial bone 4 have a cortical bone quality corresponding to a drilling resistance rc=25N (same initial slope of the curve).
- Bone prosthesis 1 has a cortical thickness (position of plateau start) of 6 mm, while prosthesis 4 has a cortical thickness (plateau start) of 1 mm.
- the bone quality of the cancellous area with the following relationship: rt = rc-|pt| can be determined.

Therefore, from these measurements, prosthesis 1 has a high cancellous bone quality corresponding to a perforation resistance rt = 16.5 N (pt = -8.5 N), while prosthesis 4 has a perforation resistance rt = 10 N (pt = -8.5 N). pt=−15N) with lower cancellous bone quality.

Polynomial curve fitting can preferably be accomplished for each of the three detection steps described above: first linear rise, then plateau, and finally again linear slope.

According to a preferred embodiment of the invention, the electrical device for controlling the implanting motor further comprises post-processed signals of the current and the model of the drilling tool used, installed in the memory of the box or peripheral device. to discrete parameters (integers) for classifying bone quality, corresponding for example to BMI (bone density) or BMD (bone mineral density) type classifications. These types of classifications are represented by continuous variables, but are actually used by assessing these values in terms of categories/ratings based on experience and statistical results that divide them into different "classes".

Therefore, it is possible to relate the measurements obtained by the proposed method to a discrete variable assessment (1, 2, 3, 4) of bone quality, thereby as a function of the risk associated with implant placement. , allowing an easy cumulative evaluation of the results obtained (e.g. quality 1 corresponding to resistant implants/very slight risk, quality 2: stable implants, low risk, quality 3: Potentially Unstable Implant, High Risk, Quality 4: Unstable Implant, Very High Risk).

According to a preferred variant of the electronic device for controlling the implanting motor, as shown in the remainder of FIG. 1, an interface is available for the transfer of data to another electronic device and the transfer tool preferably consists of a WIFI emitter to avoid any unnecessary additional cables.

Furthermore, according to a preferred embodiment variant of the device and method according to the present invention, the surgeon, directly via an interface peripheral, i.e. the console, inputs the input data constituted by the "model of the drilling tool used" into the human body. It is possible to choose among several possible models depending on the user's preferences or operational constraints. The measurement can in fact be carried out by means of a special drilling tool characterized by a cross section of diameter that varies by a factor of at least 2 along the axis of the tool, the maximum diameter preferably being Located at a distance d from the tool tip, d being between 2 mm and 5 mm. Two examples of this type of tool are presented in Figures 4a and 4b.

FIG. 4a shows a special drilling tool coupled to a contra-angle, characterized by a cross-section of variable diameter with a “minimum-maximum” profile, the portion characterized by the maximum diameter being , (for example also referred to as L _F in FIG. 5 discussed hereinafter ₎ and FIG. Typically, it is characterized by a variable diameter cross-section having a "min-max-min-max-min" profile. The special tool represented in Figure 4b results in optimal tapping of the bone hole (i.e. creating a threaded hole in the case of a standard drilling tool) and cortical-cancellous separation (like the tool represented in Figure 4a). The additional advantage of having an accurate measurement of the part is obtained.
- the "first _" portion (i.e. the portion that first enters the bone) characterized by the largest diameter (over length LF) is the "probe" and has the role of measuring the current or current derivative; Bone quality is therefore assessed and the cortical-cancellous separation is identified.
A "second" portion characterized by a maximum diameter (over length L _F2 ) if the first portion is too short (L _F <<L _F2 ) to directly produce the optimal thread of the hole has the role of completing the tapping task.

The use of the special drilling tool of FIG. 4b thus makes it possible to avoid the additional operation of tapping the bone hole to create an optimal thread for the subsequent implant. Clearly, if the penetration of the first portion of the maximum diameter (i.e., the "probe") and the corresponding evaluation of the current derivative (and/or the torque derivative) are indicative of very poor bone quality, the maximum diameter " The drilling and tapping operation can be stopped immediately before the "second" portion enters the cortical zone, thus minimizing bone lesions.

The diameter of the drill bit should be adjusted so that the drilling stage does not unduly increase the risk of improper drilling (drilling directly at excessive diameters risks overheating and/or starting to crack the bone). Optimized to reduce the number (and thus the risks associated with repetition of actions, generated vibrations and heat). Currently, most drill bit manufacturers recommend three stages of drilling.
1. Drilling with a 2.2 mm diameter drill bit.
2. Drilling with a 2.8 mm diameter drill bit.
3. Drilling with a 3.0 or 3.2 mm diameter drill bit.

Drilling quality is based on three qualitative criteria.
1. No cracks in the bone diametrically across the drilled hole.
2. The direction of the hole should be substantially perpendicular to the bone surface.
3. Low heat level in the perforated area (parameter cannot be precisely measured).

Thus, choosing between different possible drill bit profiles provides the surgeon with increased flexibility regarding the optimization of working protocol selection.

Furthermore, according to a preferred embodiment, following the results of measurements and determinations of the bone quality with which the implant has to be performed, an optimization program installed on the console for the subsequent drilling steps mentioned above: It is possible to automatically pre-select a specific optimal program based on bone quality-related results detected after a drilling operation. This makes it possible, for example, to also adjust the size of the drill bit used for subsequent drilling steps or the speed of the motor, or even determine the automatic limit of the applicable torque so as not to damage the bone. is also possible.

The devices and methods disclosed within the framework of the present invention thus make it possible to obtain a more precise quantitative measure of bone quality, in particular to measure the local thickness of cortical regions of bone.

This device and this measuring method also has the advantage that it is suitable for many commercial drilling tools and can be used in combination with motors and standard commercial contra-angles (after calibration).

This device and this method can also be used with a special drilling tool (which can be provided with an implant kit) that allows obtaining a higher measurement accuracy if the patient is considered critically ill. .

According to the preferred embodiment described so far, the quality of the bone structure is determined by a first step (A) of drilling into said bone structure with a drilling tool such as a drill bit driven by a motor; a second step (B) of simultaneously measuring the current consumption by the motor during the first step (A) of, followed by processing the current consumption signal obtained after the second step (B), a third step of obtaining the value of the torque applied to said drilling tool by a motor and a final fourth step (D), wherein the torque value obtained after the third step (C) is Correlating with the speed of rotation of the motor and the type of the drill used during the first step (A), and deducing from this correlation the relationship between the torque values obtained and the depth of the bony structure. , in a fourth step. According to this method, the relationship between the torque value and the depth of the bone structure obtained after this fourth step (D) determines the mechanical resistance to drilling of said bone structure as a function of depth. becomes even more possible.

The relationship between the torque value and the depth of the bone structure obtained after the fourth step (D) then determines the zone of substantially constant mechanical resistance to drilling and the associated level of depth, Further identification is possible by calculating the derivative of the torque value as a function of depth. The method then further includes a subsequent step of discrete-valued typological classification of the considered bony structures in direct dependence on the torque derivatives (e.g., the perforation resistances r _c and r _t of the cortical and cancellous regions, respectively). can contain.

However, according to yet another preferred embodiment of the invention, another current related value is used as input parameter, namely the current derivative. In this case, instead of measuring current values, current derivative values are directly sampled by the measuring unit.

The state diagram of FIG. 5 shows how the current derivative value is determined depending on the current depth z(t), which depends on the rotational speed of the motor, to yield a bone quality value, i.e., a bone quality value as a function of depth z. explain how to handle

The procedure is summarized by the following steps (in this detailed description, the working length L _F of the drilling tool is considered to be longer than the depth corresponding to the separation between the cortical and cancellous regions).
1. A calculated quantity z _test that specifies the actual penetration depth in the bone is initialized to zero. Di[z _test (0)] is also initialized to zero. A discrete variable, _fCT , which indicates the crossing of the separation between the cortical and cancellous regions, is also initialized to zero ( _fCT is zero until the drilling tool crosses the separation between the cortical and cancellous regions). ).
2. Before penetration into the bone, the value of the current derivative is almost zero, apart from noise fluctuations mainly due to contra-angle and motor induced. Therefore, the first logical block is clearly filled (YES). Since z(t) is less than the length of the working portion of the drilling tool (L _F ), z _test is not incremented until the drilling tool is in the bone.
3. The moment the drilling tool enters the cortical region of the bone (ie the external region of the bone) the current derivative di/dz becomes positive. The first logic block is unsatisfied (NO), and so is the second block (because the current derivative di/dz is positive). Therefore, the actual depth z-- _test is incremented (taking into account the actual speed of the tool) and the quantity Di corresponding to the incremented value of z-- _test takes the value di/dz.
4. While the drilling tool (or part thereof) is inside the cortical region (i.e. before crossing the separation between the cortical and corpus cavernosum regions), the current derivative is nearly constant (with small fluctuations due to signal noise or except for a slow and slight increase due to a slight increase in bone density inside the cortical area). The reason is that linear increments in penetration length (and contact surface between the drilling tool and cortical material) correspond to linear increments in torque and current required. The first and second logic blocks are not satisfied (both take the value "NO"). Therefore, the actual depth z - - _test is incremented and the quantity Di is either constant or takes on a new value of di/dz if the quantity Di is slightly larger than the previous one.
5. When the drilling tool reaches the separation between the cortical and cancellous regions without being fully engaged inside the cortical region, the current derivative (and torque derivative) suddenly drops (to zero or the previous to a significantly smaller positive value). Further advancement of the drilling tool inside the bone (ie the cancellous area of the bone) does not require an associated additional current supply. The first logic block is filled (YES) and the second logic block is filled as well (where the drilling tool is longer than the depth corresponding to the separation between the cortical and cancellous regions). Therefore, the actual depth z-- _test is not incremented.
6. The actual depth is not incremented until the working portion of the drilling tool is partially outside the bone (ie, the portion of the drilling tool inside the cortical area is constant). When the drilling tool is completely inside the bone and the portion of the drilling tool inside the cortical area begins to decrease, the current derivative becomes negative. The contribution of additional cancellous material contacting the drilling tool does not compensate for the reduced amount of cortical material in contact with the working portion of the drilling tool. Therefore, the first logic block is not satisfied (NO), while the second logic block is satisfied (YES: the current derivative is negative and f _CT is still zero). The actual depth z - - _test is increased, while the "incremental current derivative" Di is decreased (because the current derivative di/dz is negative). f _CT changes to 1 as the separation between the cortical and cancellous regions is reached.
7. The current derivative is negative until the working portion of the drilling tool is completely inside the cancellous area. From this point the current derivative is close to zero (aside from signal noise and slight non-uniformity). Since f _CT is 1, both the first and second logic blocks are not filled, so the actual depth is incremented until the end of the measurement.

The procedure is modified from item 5 if a special piercing tool (such as that in FIG. 4a) is used whose working portion is shorter than the depth of the separation between the cortical and corpus cavernosum regions. In this case, the current derivative suddenly drops to zero or a very low value when the working part of the drilling tool is completely inside the cortical area (i.e. before reaching the separation between the cortical and cancellous areas). . In this case, the second logic block on the right side of the state diagram is not satisfied when the current derivative is at or near zero. Therefore, the incremental current derivative Di remains constant until the working portion of the drilling tool is inside the cortical region. Also, in a special tool like FIG. 4a, items 6 and 7 remain valid. A negative value of the current derivative di/dz results in a reduction in the incremental current derivative Di, causing a reduction in the density and/or hardness of the cancellous region.

The procedure just described makes it possible to unambiguously identify the two values responsible for cortical and cancellous bone quality respectively. In addition, this makes it possible to identify the depth of the separation between the cortical and corpus cavernosum regions.

Using current derivative values instead of current values as input parameters to yield torque derivative values and thus bone quality values has the following advantages. First, this compares to methods that first need to post-process the current values to correlate them with the torque values, and then derive the torque derivative curve from these values, in comparison to the computational step is significantly reduced. Second, torque values are affected by the performance of the handpiece and the motor itself, which can change over time depending on life and lubrication conditions. Therefore, the measurements provided do not depend solely on bone density and hardness and thus their associated qualities. Third, torque measurement essentially relies on the mechanical resistance exerted by the bone on the drilling tool, spatially integrated over the entire length of the drilling tool inserted into the bone at a given moment. It is therefore not a local measurement that allows density and hardness to be determined locally in a very sharply defined spot.

This computational method therefore allows regions of uniform density and hardness, such as cancellous and cortical regions, to be more easily identified and to indicate puncture resistances r _c and r _t , respectively.

These puncture resistances r _c and r _t previously shown in FIG. 3B can be further obtained in an even more intuitive manner in the diagrams of FIGS. 6A and 6B, which show the same FIG. 4 shows a graph of current derivative as a function of depth for the same bone prosthesis when drilled by a drill bit; FIG. Indeed, the constant derivative of torque as a function of depth (z) indicates a uniform puncture resistance r _c across cortical regions rather than being derived from the initial slope. Then, when the current derivative becomes negative after the depth exceeds the length of the drill bit (i.e. 8 mm), we obtain the value |p _t |=r _c −r _t , thus the resistance within the cancellous region r _t be able to. Therefore, the measurement can be stopped at this depth as all resistance values have been determined, so the Pen _{end_of_measurement} can be set to about 9 mm as shown in FIG. 6A.

Figure 6B shows how the incremental current derivative values are directly mapped to the drilling resistance values for each of the bone types, i.e. prosthesis 1 and prosthesis 4, and therefore the bone quality It shows how it can be very easily mapped to the scale of . In this case, we have r _c1 =r _c4 approximately equal to 0.34 A/mm, r _t1 =0.22 A/mm and r _t4 =0.14 A/mm. These values correspond to values previously obtained via the spatial derivative of the torque, and the mathematical relationship between the corresponding values is
xηk _t Di=dc/dz
where x is the multiplication factor (20 if the contra-angle is 20:1 CA), η is the yield of CA, and _kt is the torque proportional to the supplied current. value) is the torque constant of the motor.

Figures 7A and 7B show drilling resistance values that can still be obtained with a special drill such as the one disclosed in Figure 4A, having a reduced length _Lf corresponding to the portion of greatest diameter. These values yield the same values for drilling resistance (in effect, FIGS. 6B and 7B are identical), but due to the reduced length of the drill going below the depth of the cortical region, the following It is possible to have advantageous properties. As soon as the drill bit is fully engaged within this zone, the current derivative drops to zero (see drop at z=0.5 in FIG. 7A) and the depth P _{The end_of_measurement} can then be just after the end of each cortical area, ie about 1.5 mm for bone prosthesis 4 and 6.5 mm for bone prosthesis 1 . As a result, the overall drilling operation can be shortened, which can also be less invasive and generate less heat due to friction.

Another advantage of employing this calculation method and this special drill using current derivative values as input values is that the respective resistance values of the cortical and cavernous regions are given by current derivative values of opposite sign. is. The crossover due to the change in sign of the current derivative makes it possible to reduce the influence of noise on the measurement.

However, it can be appreciated that regardless of the type of drill used, the use of the current derivative value as an input makes it possible to easily identify transitions between regions, in this case the current Derivative values make large jumps from one discrete value to another. Hence, the results provided are more accurate and more reliable while omitting any post-processing of the input signal.

Within the framework of the present invention, it is also possible to provide more accurate results regarding 3D modeling of bone structure quality. In fact, as shown in FIGS. 8A and 8B, the transition between regions is not sharp according to the horizontal plane, and it is quite possible that there may instead be some partial vertical overlap. The sagittal section in FIG. 8A highlights the vertical interdigitation of the corpus cavernosum and cortical regions, and the cross section in the horizontal plane AA shows the angular proportions of the superimposed corpus cavernosum.

In order to be able to quantify bone quality more precisely, the device according to the invention is preferably arranged to sample current-related values at a rate of at least 10 times per full revolution of the drill bit. If the handpiece reduction ratio is chosen to be equal to 20:1 and the motor speed is about 400 rpm, the device collects at least 5 measurements per second. The drill bit makes a full revolution every 3 seconds, so 15 measurements are available for each revolution of the drill bit. Therefore, it is possible to obtain a good angular distribution of bone quality. The distribution of the data over the full revolution of the drill bit gives the idea that the amplitude of local variation affecting density/hardness is due to different orientations.

The device for determining the quality of the bone structure preferably also includes an orientation determination system based on angle sensors in order to know the correct orientation of the contra-angle rotor and thus of the drill bit. As shown in Figures 9a and 9b, the angle sensors can be for example Hall sensors, magnetic sensors, optical sensors or electrical sensors. In this way it is possible to determine the exact orientation of the drill bit inside the bone by ensuring that the relative angular orientation of the drill bit with respect to the angular position of the motor is always known. be.

Therefore, when further providing a device for determining the quality of bone structure, comprising a non-circular asymmetric drill bit providing an extruded diameter of at least 20% greater than the average diameter of the drill bit, the It is possible to obtain a 3D view, because it is possible to know the variations in bone quality not only as a function of penetration depth, but also as a function of angular orientation. An example of such an asymmetric drill bit is shown in FIG.

According to a variant embodiment of the invention, the device for determining the quality of bone structure further comprises a calibration and benchmarking tool to Allows to define classification criteria. An example of such a calibration system is shown in Figure 11, where the left part of the figure shows different benchmark parts of the material to be drilled, and the right part has a torque meter, an accelerometer and a video camera as modules. Fig. 2 shows a schematic diagram of a contra-angle handpiece fitted in the form of or not.

As an example, the following calibration procedure can be performed.
- Collect images of the drill bit via a camera integrated into the dental unit, tabletop control unit, or modular calibration system. The tail of the drill bit is normalized, which then facilitates obtaining the scale of the image and thus extracting the working diameter and working length of the drilling tool.
- Measuring the current derivative data when drilling into a sample of material (here four samples: Q1, Q2, Q3, Q4) with a mounted drill. Initial current derivative measurements are sufficient to set bone quality parameters.
- As an alternative to the calibration step described above, the torque applied to the tip of the drill bit (via a torque meter, such as a sleeve out of resin, which applies adjustable friction to the top of the drill) is combined with current derivative data. Measure at the same time. In such cases, it is not necessary to have multiple blocks of material, one is sufficient if a correlation scale between torque values and baseline bone quality is established.
- Control rotation speed via accelerometer and video camera when drilling to check speed consistency. If the speed is erratic, after-sales service intervention is required or the drill bit is deemed unsuitable.

In this way, no updating of the database and/or creation of an after-sales service force is required when new drill bits, new handpieces, or new motors conforming to this device enter the market.

From the foregoing discussion, it can be seen that the features of the preferred embodiments detailed above can be combined as desired, particularly for drilling, regardless of the input parameters used to calculate the torque derivative value and hence bone quality. • It will be appreciated that features on bits can be used.

Claims (11)

A device for determining the quality of a bone structure, comprising a device for controlling a motor kinematically coupled to a drilling tool such as a drill bit,
The apparatus for determining quality of said bone structure comprises:
a measurement unit for instantaneously measuring a current derivative value consumed by the motor during a drilling operation, wherein the current derivative value is directly sampled by the measurement unit;
a processing unit suitable for processing data collected by said measurement unit concurrently with said drilling operation, said processing unit also suitable for processing measured current derivative values; The processing obtains a value of the derivative of the torque applied by the motor to the drilling tool, and combines the obtained torque derivative value with the speed of rotation of the motor and the type of drill used during the drilling operation. correlating and from said correlation estimating the relationship between said obtained torque derivative value and the depth of said bone structure, said torque derivative value corresponding to drilling resistance and thus bone quality. stipulate,
wherein said current derivative value directly yields a torque derivative value and thus a bone quality value as a function of depth ;
where the current derivative value is defined as di/dz, where i is the current, z is the depth, and the working part of the drilling tool is the part of said drilling tool that can cut bone material. when z is a value between 0 and the working length of said drilling tool,
Apparatus for determining the quality of bone structure, wherein the measurement unit is configured to sample the current derivative values at least ten times per full rotation of the drill bit. 2. Determining the quality of bone structure according to claim 1, wherein a constant current derivative value over a given depth allows identifying regions of uniform density and hardness classified into bone quality classes. equipment for The apparatus for determining the quality of said bone structure further comprises a drill bit, said drill bit having a variable diameter profile ranging between a minimum value and a maximum value, said minimum value and said maximum value. 3. A device for determining the quality of bone structures according to claim 1 or 2, wherein the ratio between the values is at least equal to two. further comprising an orientation determination system for the drill and an angle sensor for the rotor of the contra-angle to know the correct orientation of the drill bit ;
The orientation determination system is a system for changing the orientation of the drill bit step-by-step while connected to the rotor to determine the angular position of the drill bit with respect to the motor, and the angle sensor detects the angle of the motor. 4. A device for determining the quality of bone structure according to any one of claims 1 to 3, which measures the relative angular position of the drill bit with respect to the position . 5. The bone structure of any one of claims 1-4 , wherein the drill bit is an asymmetric section drill bit providing an extruded diameter at least 20% greater than the mean diameter of the drill bit. equipment for determining the quality of further comprising a calibration and benchmarking tool adapted to the contra-angle handpiece, drill bit and/or motor , wherein said benchmarking tool is part of a drilling rig and said benchmarking tool is For determining the quality of bone structures according to any one of claims 1 to 5 , wherein the tool consists of a set of materials to be drilled that mimic artificial bones of known hardness. Device. The apparatus for determining the quality of the bone structure further comprises a drill bit, the drill bit removably mounted on a contra-angle handpiece, the contra-angle handpiece comprising: 7. A device for determining the quality of bone structure according to any one of claims 1 to 6 , which determines a predetermined gear ratio and is adaptable to a plurality of different types of drills. 8. Any of claims 1 to 7 , further comprising a console equipped with a display unit and a control interface allowing the surgeon to determine the type of drill used and set the speed of rotation of the motor. A device for determining the quality of a bone structure according to any one of the preceding clauses. 9. For determining the quality of bone structure according to claim 8 , wherein the console automatically pre-selects an appropriate specific program based on the bone quality-related results detected after the drilling operation. equipment. 10. A device for determining the quality of bone structures according to any one of claims 1 to 9 , further comprising a wireless communication interface for transmission of measurement data. Such that the device yields two distinct values in the current derivative values responsible for cortical and cancellous bone respectively, and locates the depth of the separation , which is the transition from cortical to cancellous bone. A device for determining the quality of bone structures according to any one of claims 1 to 10 , configured.

Images